1. Field of the Invention
The present invention relates to an immersion-type temperature measuring apparatus using a thermocouple, for measuring temperature of a melt such as a molten metal or a molten slag in a furnace such as an induction heating furnace.
2. Related Art Statement
Temperature of a melt such as a molten metal or a molten slag in a furnace such as an induction heating furnace exerts an important effect on operations and product quality. It is therefore necessary to periodically measure temperature of a melt such as a molten metal or a molten slag in a furnace such as an induction heating furnace.
For the purpose of measuring temperature of a molten metal in a furnace, an immersion-type temperature measuring apparatus using a thermocouple as shown in FIGS. 1 and 2 has widely been employed. FIG. 1 is a schematic vertical sectional view illustrating part of a conventional immersion-type temperature measuring apparatus using a thermocouples for measuring temperature of a melt. In FIG. 1, 1 is a temperature sensor, 2 is a paper tube, and 3 is a ceramic fiber tube. The paper tube 2 is covered with the ceramic fiber tube 3 which is a heat-insulator, and is formed integrally with the temperature sensor 1. FIG. 2 is a schematic vertical sectional view illustrating details of the above-mentioned temperature sensor 1. In FIG. 2, combination of 4 and 5 is a thermocouple comprising platinum and a platinum-rhodium alloy, 6 is a quartz glass protecting tube for protecting the thermocouple 4, 5 from a melt such as a molten metal or a molten slag, combination of 7 and 8 is an extension lead wire for connecting the thermocouple 4, 5 with a measuring instrument not shown, 9 is a housing for receiving a junction between the thermocouple 4, 5 and the extension lead wire 7, 8, and 10 is a cap made of iron or aluminum, having at least one through-hole, for protecting the quartz glass protecting tube 6 from a melt such as a molten metal or a molten slag. As shown in FIG. 1, furthermore, the housing 9 and the extension lead wire 7, 8 are protected by the paper tube 2 and the ceramic fiber tube 3, which have a heat-insulating function.
By means of the above-mentioned conventional immersion-type temperature measuring apparatus using the thermocouple, temperature of a molten metal is measured as follows.
An upper portion of the paper tube 2 of the conventional immersion-type temperature measuring apparatus using the thermocouple as shown in FIG. 1, is vertically supported by means of a holder not shown. A portion of the temperature sensor 1 covered with the cap 10 vertically descends toward a molten metal by actuating a lift not shown, and is immersed into the molten metal. When the portion of the temperature sensor 1 covered with the cap 10 is immersed into the molten metal, the molten metal penetrating into the cap 10 through at least one through-hole thereof comes into contact with the quartz glass protecting tube 6. A thermoelectromotive force corresponding to temperature of the molten metal is detected by the thermocouple 4, 5 covered with the quartz glass protecting tube 6, and temperature of the molten metal is determined by a measuring instrument not shown through the extension lead wire 7, 8 (hereinafter referred to as the "prior art").
The prior art has however the following problems.
The quartz glass protecting tube 6 covering the thermocouple 4, 5, while having a high thermal shock resistance, has a low erosion resistance to a molten metal, leading to rapid erosion of the protecting tube 6 when immersed into the molten metal. Consequently, a first run of measurement for a short period of time causes the molten metal to penetrate into the protecting tube 6, thus resulting in break-down of the thermocouple 4, 5. It is therefore necessary to replace the temperature sensor 1, the paper tube 2 and the ceramic fiber tube 3 after every run of measurement. This requires much time for a replacement operation and is therefore uneconomical.
Under such circumstances, there is a strong demand for development of an immersion-type temperature measuring apparatus using a thermocouple, which permits multiple runs of measurement of temperature of a melt such as a molten metal or a molten slag in a furnace such as an induction heating furnace for a long period of time with the use of a single temperature sensor, and easy replacement of the temperature sensor, but such an immersion-type temperature measuring apparatus has not as yet been proposed.